#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define LINE_MAX 1024

int convert_utf8_to_windows1251(const char* utf8, char* windows1251, size_t n);

int main(int argc, char ** argv)
{
	//printf("start %s\n", argv[0]);

	if (argc <= 1) {
		printf("forgot file name for conversion");
		exit(EXIT_FAILURE);
	}

	FILE* file = fopen(argv[1], "r");
	if (!file) {
		perror("can't open file");
		exit(EXIT_FAILURE);
	}

	while(!feof(file)) {
		char buff[LINE_MAX] = {0};
		if (!fgets(buff, LINE_MAX, file)) {
			perror("can't read line from file");
			exit(EXIT_FAILURE);
		}

		char output[LINE_MAX] = {0};
		if (!convert_utf8_to_windows1251(buff, output, LINE_MAX)) {
			printf("can't convert line: %s\n", buff);
			exit(EXIT_FAILURE);
		}
		printf("%s", output);
	};

	return EXIT_SUCCESS;
}

typedef struct ConvLetter {
	char	win1251;
	int		unicode;
} Letter;

static Letter g_letters[] = {
	{0x82, 0x201A}, // SINGLE LOW-9 QUOTATION MARK
	{0x83, 0x0453}, // CYRILLIC SMALL LETTER GJE
	{0x84, 0x201E}, // DOUBLE LOW-9 QUOTATION MARK
	{0x85, 0x2026}, // HORIZONTAL ELLIPSIS
	{0x86, 0x2020}, // DAGGER
	{0x87, 0x2021}, // DOUBLE DAGGER
	{0x88, 0x20AC}, // EURO SIGN
	{0x89, 0x2030}, // PER MILLE SIGN
	{0x8A, 0x0409}, // CYRILLIC CAPITAL LETTER LJE
	{0x8B, 0x2039}, // SINGLE LEFT-POINTING ANGLE QUOTATION MARK
	{0x8C, 0x040A}, // CYRILLIC CAPITAL LETTER NJE
	{0x8D, 0x040C}, // CYRILLIC CAPITAL LETTER KJE
	{0x8E, 0x040B}, // CYRILLIC CAPITAL LETTER TSHE
	{0x8F, 0x040F}, // CYRILLIC CAPITAL LETTER DZHE
	{0x90, 0x0452}, // CYRILLIC SMALL LETTER DJE
	{0x91, 0x2018}, // LEFT SINGLE QUOTATION MARK
	{0x92, 0x2019}, // RIGHT SINGLE QUOTATION MARK
	{0x93, 0x201C}, // LEFT DOUBLE QUOTATION MARK
	{0x94, 0x201D}, // RIGHT DOUBLE QUOTATION MARK
	{0x95, 0x2022}, // BULLET
	{0x96, 0x2013}, // EN DASH
	{0x97, 0x2014}, // EM DASH
	{0x99, 0x2122}, // TRADE MARK SIGN
	{0x9A, 0x0459}, // CYRILLIC SMALL LETTER LJE
	{0x9B, 0x203A}, // SINGLE RIGHT-POINTING ANGLE QUOTATION MARK
	{0x9C, 0x045A}, // CYRILLIC SMALL LETTER NJE
	{0x9D, 0x045C}, // CYRILLIC SMALL LETTER KJE
	{0x9E, 0x045B}, // CYRILLIC SMALL LETTER TSHE
	{0x9F, 0x045F}, // CYRILLIC SMALL LETTER DZHE
	{0xA0, 0x00A0}, // NO-BREAK SPACE
	{0xA1, 0x040E}, // CYRILLIC CAPITAL LETTER SHORT U
	{0xA2, 0x045E}, // CYRILLIC SMALL LETTER SHORT U
	{0xA3, 0x0408}, // CYRILLIC CAPITAL LETTER JE
	{0xA4, 0x00A4}, // CURRENCY SIGN
	{0xA5, 0x0490}, // CYRILLIC CAPITAL LETTER GHE WITH UPTURN
	{0xA6, 0x00A6}, // BROKEN BAR
	{0xA7, 0x00A7}, // SECTION SIGN
	{0xA8, 0x0401}, // CYRILLIC CAPITAL LETTER IO
	{0xA9, 0x00A9}, // COPYRIGHT SIGN
	{0xAA, 0x0404}, // CYRILLIC CAPITAL LETTER UKRAINIAN IE
	{0xAB, 0x00AB}, // LEFT-POINTING DOUBLE ANGLE QUOTATION MARK
	{0xAC, 0x00AC}, // NOT SIGN
	{0xAD, 0x00AD}, // SOFT HYPHEN
	{0xAE, 0x00AE}, // REGISTERED SIGN
	{0xAF, 0x0407}, // CYRILLIC CAPITAL LETTER YI
	{0xB0, 0x00B0}, // DEGREE SIGN
	{0xB1, 0x00B1}, // PLUS-MINUS SIGN
	{0xB2, 0x0406}, // CYRILLIC CAPITAL LETTER BYELORUSSIAN-UKRAINIAN I
	{0xB3, 0x0456}, // CYRILLIC SMALL LETTER BYELORUSSIAN-UKRAINIAN I
	{0xB4, 0x0491}, // CYRILLIC SMALL LETTER GHE WITH UPTURN
	{0xB5, 0x00B5}, // MICRO SIGN
	{0xB6, 0x00B6}, // PILCROW SIGN
	{0xB7, 0x00B7}, // MIDDLE DOT
	{0xB8, 0x0451}, // CYRILLIC SMALL LETTER IO
	{0xB9, 0x2116}, // NUMERO SIGN
	{0xBA, 0x0454}, // CYRILLIC SMALL LETTER UKRAINIAN IE
	{0xBB, 0x00BB}, // RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK
	{0xBC, 0x0458}, // CYRILLIC SMALL LETTER JE
	{0xBD, 0x0405}, // CYRILLIC CAPITAL LETTER DZE
	{0xBE, 0x0455}, // CYRILLIC SMALL LETTER DZE
	{0xBF, 0x0457} // CYRILLIC SMALL LETTER YI
};



int convert_utf8_to_windows1251(const char* utf8, char* windows1251, size_t n)
{
	int i = 0;
	int j = 0;
	for(; i < (int)n && utf8[i] != 0; ++i) {
		char prefix = utf8[i];
		char suffix = utf8[i+1];
		if ((prefix & 0x80) == 0) {
			windows1251[j] = (char)prefix;
			++j;
		} else if ((~prefix) & 0x20) {
			int first5bit = prefix & 0x1F;
			first5bit <<= 6;
			int sec6bit = suffix & 0x3F;
			int unicode_char = first5bit + sec6bit;

			if ( unicode_char >= 0x410 && unicode_char <= 0x44F ) {
				windows1251[j] = (char)(unicode_char - 0x350);
			} else if (unicode_char >= 0x80 && unicode_char <= 0xFF) {
				windows1251[j] = (char)(unicode_char);
			} else if (unicode_char >= 0x402 && unicode_char <= 0x403) {
				windows1251[j] = (char)(unicode_char - 0x382);
			} else {
				int count = sizeof(g_letters) / sizeof(Letter);
				for (int k = 0; k < count; ++k) {
					if (unicode_char == g_letters[k].unicode) {
						windows1251[j] = g_letters[k].win1251;
						goto NEXT_LETTER;
					}
				}
				// can't convert this char
				return 0;
			}
NEXT_LETTER:
			++i;
			++j;
		} else {
			// can't convert this chars
			return 0;
		}
	}
	windows1251[j] = 0;
	return 1;
}
